High power electrical bushing having a vacuum switch encapsulated therein

ABSTRACT

A molded plastic bushing for high electrical power applications is provided with an encapsulated vacuum switch which is operable to interrupt current in the circuit through the bushing. The combination bushing and vacuum switch are characterized by having an end-to-end withstand voltage rating that is at least twice as great as the withstand voltage rating of the switch in an unencapsulated state. The bushing-switch combination is further characterized by affording an ideal handling and support mechanism for the vacuum switch container, so that large contactclosing pressures can be employed to actuate the switch, without danger of damage to the switch or its encapsulation.

United States Patent [191 Nonken May 21, 1974 [75] Inventor: Gordon C. Nonken, Pittsfield, Mass.

[73] Assignee: General Electric Company,

Pittsfield, Mass.

[22] Filed: Aug. 23, 1971 [21] Appl. No.: 173,871

[52] US. Cl 200/144 B [51] Int. Cl. IIOlh 33/66 [58] Field of Search 200/ [44 B [56] References Cited UNITED STATES PATENTS 3,426,168 2/1969 Hansen 200/144 B FOREIGN PATENTS OR APPLICATIONS l.030,798 5/1966 Great Britain ZOO/I44 B Primary Examiner-Robert S. Macon Attorney, Agent, or FirmFrancis X. Doyle; Volker R. Ulbrich; John J. Kelleher 5 7 ABSTRACT A molded plastic bushing for high electrical power applications is provided with an encapsulated vacuum switch which is operable to interrupt current in the circuit through the bushing. The combination bushing and vacuum switch are characterized by having an end-to-end withstand voltage rating that is at least twice as great as the withstand voltage rating of the switch in an unencapsulated state. The bushing-switch combination is further characterized by affording an ideal handling and support mechanism for the vacuum switch container, so that largecontact-closing pressures can be employed to actuate the switch, without danger of damage to the switch or its encapsulation.

9 Claims, 3 Drawing Figures ,"yseseeeeemeeemw PATENTEUMAY 21 1914 3,812,814

SHEET 2 0f 2 HIGH POWER ELECTRICAL BUSHING HAVING A VACUUM SWITCH ENCAPSULATED THEREIN BACKGROUND OF THE INVENTION It is well known in the field of electric power distribution to utilize vacuum circuit interrupters or switches to perform a large variety of different interrupting or switching functions. However, because of the inherent cost of prior art vacuum switches, coupled with the relatively fragile construction of most vacuum switch bottles, the applications of such switches have tended to be limited to devices in which a large number of circuit interrupting operations are normally required. Thus, the relative cost of the switches can be justified over their useful life span. Common prior art applications of vacuum switches are in high voltage power circuit breakers and in low voltage switching circuits calling for numerous circuit interrupting operations.

In addition to the limitations of expense and relatively fragile switch structure, prior art high voltage vacuum switches are limited, by inherent relatively large size, to applications that can accommodate the switches with adequate housing space and support structure. All of these characteristic features of conventional vacuum art switches served to prevent them from being utilized extensively as switching means in underground power distribution systems. The normal requirements of a switching function in such a system are thatit be; competitively priced, rugged in construction, and small enough to be conveniently mounted in underground vault areas.

Some of these system requirements could be met by combining a vacuum switch with other components that afford different functions in the system. in fact, attempts have been made in the prior art to combine the features of high voltage vacuum circuit interrupters and submersible oil-filled circuit interrupters to provide vacuum switching capabilities for underground power distribution systems. For example, US. Pat. No. 3,471,669 Curtis, issued Oct. 7, 1969 and entitled Encapsulated Switch Assembly for Underground Electric Distribution Service discloses the use of a relatively high voltage vacuum switch in combination with an underground power distribution switching module, which incorporates plug-on connector terminals that facilitate connection of underground power cable terminations to the switch. However, the encapsulated switch disclosed in that patented device has the disadvantages of relatively high cost and cumbersome size that were noted above. Another example of such a prior art combination is shown in U.S. Pat. No. 3,594,524, which issued July 20, 1971 and is assigned to the assignee of the present invention. Again, this patent shows an oil-filled tank with a vacuum circuit breaker submerged in the oil and electrically connected between a pair of plug-on type bushings that are mounted on the tank.

A primary object of the present invention is to overcome the disadvantages outlined above thereby to provide a practical vacuum switching device in combination with a rugged plastic bushing for underground electric power distribution systems.

Another object of the invention is to provide a plastic bushing combined in an integral assembly with an encapsulated vacuum switch thereby to reduce the overall cost of the combined bushing and switching functions, while simultaneously obtaining the objective of reduced size and minimized space requirements for a vacuum switching function in an underground power distribution system.

Yet another object of the invention is to provide a vacuum switch encapsulated in a plastic bushing in a manner such that the end-to-end withstand voltage rating of the bushing is at least twice as great as the endto-end voltage rating of the unencapsulated vacuum switch.

A still further object of the invention is to provide a ruggedly constructed, low cost vacuum switch and bushing device that affords an ideal handling and mounting support for the vacuum switch so that the switch contacts can be closed under high pressure without damaging either the switch or the bushing.

Additional objects and advantages of the invention will become apparent to those skilled in the art from the description of it that follows taken in conjunction with the attached drawings.

SUMMARY OF THE INVENTION The invention is related tothe field of underground power distribution switching and bushing devices, and more particularly comprises a plastic bushing that is adapted to be mounted in an underground power'transformer or similar device, and which encapsulates a low cost vacuum switch, In one preferred embodiment of the invention, a uniquely low-cost vacuum switch is encapsulated in the molded dielectric of a bushing, which also has a bushing-mounting flange encapsulated in its outer surface. The bushing-mounting flange enables the bushing to be rigidly mounted in operating position on the wall of an underground transformer tank in hermetically sealed relationship with the tank. The end-toend withstand voltage of the vacuum switch is at least doubled by the encapsulating dielectric of the bushing. In an alternative embodiment of the invention, a plurality of vacuum switches are encapsulated in a molded bushing, thereby to afford a combination of switching functions and circuit connections.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view, partly in cross section, of a bushing and a vacuum switch encapsulated therein, pursuant to the teaching of the present invention.

FIG. 2 is a side elevation view showing, in reduced scale, a combinationbushing and vacuum switch similar to that illustrated in FIG. 1, and also showing a side elevation view of an unencapsulated vacuum switch similar to that embodied in the device depicted in FIG. 1.

FIG. 3 is a diagrammatic illustration of a side elevation view of a multi-terminal bushing having a plurality of vacuum switches encapsulated therein pursuant to the teaching of an alternative embodiment of my invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1 of the attached drawing, it will be seen that there is shown a high power electrical bushing having a vacuum switch encapsulated therein, pursuant to the teaching of the invention. The bushing 1 comprises an elongated, molded housing 1a of electrically insulated epoxy resin. the particular resin used to form the bushing 1 will be described in greater detail below with reference to particular embodiments of the invention. As illustrated in FIG. 1, the housing 1a is formed to have a frusto-conical surface 1b at one of its ends. The surface lb is adapted to receive an electric cable termination connector housing (not shown) in watertight relationship therewith.

The use of such plug-on electrical termination connectors is well known in the field of power distribution, and the use of frusto-conical, cooperating sealing surfaces between adjacent conductor junctions has become standardized. An example of such a cable connector coupling is shown in US. Pat. No. 3,55 l ,587-- Propst, entitled, Inclined Bushing for Transformers and Related Devices, which issued Dec. 29, i970 and is assigned to the assignee of the present invention.

In order to rigidly mount the bushing l in a desired operating position relative to a transformer tank or other structure, through which the bushing is intended to conduct electricity, a sturdy mounting means comprising an annular steel flange 2 is secured to the housing In at a point intermediate th respective ends thereof. The inner circumferential surface 2:; of the flange 2 is molded in water-tight relationship with the housing la, while the outer peripheral edge 2b of flange 2 is adapted to be welded to a steel supporting frame, such as the portion of a frame 3 3 which is depicted in FIG. 1. Those familiar with the manufacture of plastic bushings and their associated mounting means will understand that it may be desirable to coat the inner surface 2a of flange 2 with a resilient layer of bonding material prior to molding the flange 2 into the housing la. Such resilient layer of bonding material serves to protect the housing 1a from being cracked due to the differences in coefficients of expansion between the flange 2 and the epoxy resin of housing la.

The vacuum switch 4 which is mounted within the housing 1a during a suitable molding operation, contains several characteristic features that make it particularly suitable for use with the disclosed plastic bushing l. Specifically, switch 4 comprises a generally cylindrically shaped hollow ceramic wall member 5 that is substantially stronger than the glass or thin metal wall members conventionally used to form the vacuum bottles of vacuum switches. First and second metal end caps, 6 and 7 respectively, are sealed to opposite ends of the wall member 5, thereby to define a vacuum chamber 4a.. In this embodiment of the invention the end caps 6 and 7 are formed of electrically conductive copper, but other materials may be used in different embodiments of the invention.

Pursuant to the present invention, the ceramic of wall member 5 is a high alumina ceramic, i.e., its alumina content is in the range of 9099+ percent. In the pre ferred embodiment disclosed herein, the alumina content is in the range of 94-96 percent because this particular composition helps assure a high quality seal for the vacuum chamber. It will be understood that a conventional ceramic-'to-metal sealing process is used to form an air-tight seal between the wall member 5 and end caps 6 and 7. A first contact 8 is mounted inelectrically conducting, fixed relationship on the first end cap 6 and a second contact 9 is mounted on an electrically conductive, mechanically operable rod member 10 for relative movement with respect to the second end cap 7. As is conventional in the art of vacuum switch manufacture, means defining an aperture 11 through the second end cap 7 are provided for receiving the rod member 10 therethrough. In order to seal the aperture 11 and thereby define a vacuum chamber with the wall member 5 and end caps 6 and 7, a flexible bellows 12 is mounted in sealing relationship between the second end cap 7 and the rod member 10. It will be appreciated that the bellows 12 is suitably flexible to afford relative movement between the rod member 10 and the second cap member 7, which is sufficient to allow the movable contact 9 to be opened and closed with respect to fixed contact 8. Such bellows are well known in the vacuum switch art and any conventional material may be used'to form the bellows 12.

Of course, the rod member 10 is mounted to extend a predetermined distance beyond both sides of the bellows l2 so that the contact 9 can be moved in a predetermined range with respect to the fixed contact 8, and so that a suitable operating-linkage can be coupled to the lower end 10a of rod member 10 to effect such movement. In order to complete the electrical circuit formed through bushing 1, a suitable electrical conduc tor 8a, which in this embodiment of the invention comprises a threaded copper rod, is mounted in the bushing when it is molded. The conductor 8a is connected between the first end cap 6 and the small diameter end of the frusto-conical surface lb. Thus, an electrical circuit is formed through the contacts 8 and 9 of switch 4, when they are in engagement. and'extends from the upper end of the bushing through the rod member 10 to the lower end of the bushing. Thus, it will be seen that a characteristic feature of the present invention is to increase the end-to-end flashover voltage rating of the vacuum switch 4, appreciably beyond its flashover rating in an unencapsulated state. This objective is accomplished by spacing the unexposed electrical conductors 8a and 10 at opposite ends of the bushing l at least twice as far apart, as measured along the outer surface of bushing l, as these conductors would be separated in air-creep distance by the end caps 6 and 7 and wall member 5 of the vacuum switch 4. Accordingly, the end-to-end flashover withstand rating of the combination bushing and vacuum switch of the invention is at least twice as great as the withstand rating of the vacuum switch 4, per se. This means that a smaller, and therefore less expensive to manufacture, vacuum switch may be employed in this combination, thereby to attain part of a major objective of low cost manufacture.

ln order to assure the electrical integrity of the seal between the wall member 5'of switch 4 and the molded epoxy resin of housing la, it is necessary to forma voidfree seal between these components. I have found that such a seal may be obtained by using a soft epoxy resin that has amodulus of elasticity which enables it to expand and contract with the vacuum switch 4 without becoming separated therefrom. Alternatively, a hard epoxy resin may be used to form the housing 1a around switch 4, if a thin layer of resilient material 13 is mounted between the wall member 5 and housing 1a when the housing la is molded. To form such a layer of resilient material 13, the wall member 5 may be coated with either a cured or uncured layer of bonding material similar to that referred to above with reference to the surface 2a of steel flange 2, prior to molding the epoxy resin housing la around the vacuum switch 4. If desired, a further description of a suitable resilient material for such a layer 13 can be obtained from a reading of US. Pat. No. 3,388,211 Nichols and Nonken, which issued June 1 l, 1968 and is assigned to the assignee of the present invention.

Those skilled in the field of plastic moldings will understand that the range of elasticities of plastic resins varies greatly. However, in order to further define the present invention, it should be understood that, as used above, the term soft" epoxy is intended to mean an epoxy having a modulus of elasticity at 25C that is in the range of 7,000 to 80,000 PSI. An example of such an epoxy resin is the Gepol family of resins that is manufactured by General Electric Company at its Insulator Products Department in Baltimore, Md. In the preferred embodiment described herein, the term hard epoxy resin is intended to define resins having a modulus of elasticity at 25C that is in the range of 2.7 X PSI, i an order of 10. More generally, the materials referred to as hard epoxies are made by reacting a commercially available epoxy resin such as those sold by Shell Chemical Company under the trade name Epon Resins, or those sold by the Geigy-Ciba Corp. as Araldite Resins, with a multi-functional hardener such as a polyamine or a dibasic acid anhydride. A typical example would be the reaction product of a technical grade of the diglycidyl ether of 2,2 diphenylol propane (Epon 826) with metaphenylene diamine or with hexahydrophthalic anhydride. After cure, such materials will typically have a modulus of elasticity of 5 X 10 to l X 10 PSI.

It is common practice to incorporate into such compounds high proportions of inorganic fillers, such as silica flour, which serve such useful purposes as reducing cost, reducing thermal coefficient of expansion, increasing thermal conductivity, etc. The incorporation of such inorganic fillers will further increase the modulus of elasticity into a range as high as 5 X 10 PSI.

On the other hand, the materials described herein as soft" epoxies are those made by reacting the same types of epoxy resins with hardening systems which promote flexibility. Examples of such hardening systems are (1) acid terminated polyesters described in US. Pat. No. 2,712,535- Fisch, which issued July 5, 1955 and is assigned to Ciba, Ltd., of Switzerland; (2) combinations of dibasic anhydrides such as hexahydrophthallic anhydride with polyethylene or polypropylene glyco s.

Many examples of hard epoxies (as the term is used herein) are described in the Handbook of Epoxy Resins," Lee & Neville, in Chapters 8, 9, 10, 11, and 12 and examples of soft epoxies are given in Chapter 16 of the same reference.

The coating of flexible material 13 can be any of a variety of elastic materials, such as the material noted above with reference to the Nichols and Nonken patent. For the purpose of the present invention, it is only necessary that the material be flexible and that it ad here to both the switch 4 and the encapsulating epoxy of housing 1a. Also, the layer 13 must be free of voids material 13 is approximately 0.005 inch. However, it has been found that it is possible to form a coating up to 0.25 inch thick and still obtain relatively void-free results. The disadvantage of such a thick coating is that it is prohibitively expensive to manufacture; thus, it is not ideally suited for the present invention.

A further important feature of the combination bushing and switch of the preferred embodiment of the invention is that the epoxy resin of housing la should be at least 0.13 inch thick over its entire surface area, which encapsulates the ceramic wall member 5, so that a high stand-off voltage between the conductor 80 and rod member 10 will not puncture the resin and cause a short circuit of the switch 4. Equally as important, it is necessary that the bushing 1 be rugged in construction so that it can withstand the strong mechanical forces exerted against it when a cable connector is clamped onto the upper end of the bushing, or when a contact closing force is exerted on rod member 10. Thus, the foregoing minimum thickness of the walls of housing 1a around the vacuum switch 4 has been found to be necessary.

In order to further simplify the construction of the vacuum switch 4, thereby to better enable it to obtain the objectives of the present invention, I have found that only one of the contacts 8 or 9 needs to be formed of a relatively expensive anti-welding alloy in order to enable the switch 4 to have a reasonable life in a normal application on an underground power distribution system. Therefore, in the preferred embodiment of the invention, the first contact 8 is formed of copper while the second contact 9 is formed of an anti-welding alloy of copper and one to five percent bismuth. This results in an appreciable cost reduction that further adapts the invention for use on electric power distribution systems. It will be understood that other anti-welding alloys may be used in alternative embodiments of the invention.

Finally, I have found that a novel shielding arrangement may be used within the vacuum switch 4 in order to provide adequate shielding, at'a desirably economical price. Specifically, l have found that a single generin order to avoid corona problems. Further examples of suitable materials which have proven to be successful in this application are polyurethane (BM-221 Comp.),'

ally cylindrically shaped hollow shield 14 that is mounted on the first end cap member 6 to extend beyond the inner end of the first contact 8 to a point where it terminates in a plane that is positioned between the contacts when the movable contact is in its maximum, spaced-apart relationship with respect to the fixed contact 8, affords adequate shielding for the intended application of the invention. Prior to the present invention, it was normal practice to use considerably more expensive shielding arrangements. For example, in high voltage vacuum switches, such as those used in circuit breaker applications, it was, and still is, common practice to use a relatively long shield member mounted around both contacts, at opposite ends of the vacuum chamber. Also, it is relatively common practice to use an isolated shield that is suspended from the insulated sidewall of the vacuum chamber where it surrounds the entire gap area formed by the open contacts. Of course, such structures are relatively expensive and thus are unsuited to application in the pres ent invention.

Now that the basic features of the preferred embodiment of the invention have been described, reference may be had to FIG. 2 of the drawing, in order to more clearly visualize the relative overall size of the bushing 1 and the vacuum switch 4 which is normally encapsulated therein, pursuant to the invention. As is clearly seen in this drawing, the end-to-end length of the bushing 1 is at least twice as great as the end-to-end length of the ceramic wall member of the switch 4, across which a high voltage flashover could occur when the switch 4 is in its unencapsulated state. This illustration should graphically demonstrate one of the major advantages of the present invention; namely, the increased flashover rating afforded for a relatively inexpensive-to-manufacture vacuum switch when such a switch is encapsulated within a dielectric plastic bushing, pursuant to the teaching of the invention.

It should be apparent to those skilled in the art, from the foregoing description of a preferred embodiment of the invention, that various modifications and improvements of the invention can be made without departing from its true scope. Turning now to FIG. 3 of the drawing, it will be seen that there is shown one such extension of the teachings of the invention. In FIG. 3, like reference numerals (with prime symbols) are used to designate component parts equivalent in function to those described above, with reference to the embodiment of the invention shown in FIG. 1.

Basically, the embodiment of the invention depicted in FIG. 3 comprises a multi-terminal high power electrical bushing 1 that has a pair of vacuum switches 4' and 4 encapsulated within it. In addition, a gas operated switch which may be similar in structure and function to the quick-make, quick-break switch disclosed in US. Pat. No. 3,542,986-Kotski, which issued Nov. 24, 1970 and is assigned to the assignee of the present invention, may be used in the bushing. It will be understood that the molded epoxy resin housing In is formed of a material similar to one of those described above, and is formed to have apair of frustoconical surfaces lb and lb" extending from an outer surface thereof at spaced-apart points, so that these frusto-conical surfaces are adapted to receive electrical cable termination housings in watertight sealing relationships, in the manner discussed above with reference ,to the embodiment discussed with reference to FIG. 1. Also, a steel flange 2' is partially molded into the housing la and extends around the perimeter thereof, so that its outer edge 2b can be welded to a steel tank 16 in order to position one end of the molded housing 1a within the tank, thereby to form a gas-tight seal around the housing. In this embodiment of the invention, an electrical insulating gas, such as as Freon, is disposed in the tank 16 around the enclosed end of housing la to insulate the mechanical operating mechanisms 17 and 17a which are coupled, respectively, to the contact-operating rods 10 and 10".

Of course, each of the switches 4 and 4" comprise a generally cylindrically shaped, hollow wall member 5' and 5" and first and second metal end caps 6-7 and 6"-7", which are sealed respectively to opposite ends of the wall members 5' and 5", thereby to define vacuum chambers within these wall members in the manner discussed above with reference to FIG. 1. Also,

each switch contains a first contact 8 and 8'' respec tively that is mounted in fixed relationship on the end caps 6' and 6", and a pair of second contacts 9 and 9" respectively mounted on electrically conductive, mechanically operable rod members 10 and 10 for relative movement with respect to the second end caps 7' and 7". Finally, a pair of flexible bellows l2 and 12" u are mounted in sealing relationship between the respective second end caps 7 and 7" and the rod members 10' and 10" thereby to seal the apertures 11 and 11" defined through the second end caps 7 and 7". Of course, a pair of electrical conductors 8 a and 8a" are mounted respectively in the frusto-conical portions lb and 1b" respectively of molded housing la to form electrical circuits from the resepctive first end caps 6' 6" to the small diameter ends of said surfaces.

Any suitable mechanically operable mechanism may be mounted in the tank 16 and connected to the rod members l0-l0" for moving them to open and close the respective pairs of contacts 89 and 8"9". The significant aspect of this embodiment of the invention is the provision of a plurality of vacuum switches within a single molded epoxy resin bushing, in order to demonstrate the flexibility of the present invention for use in various underground power distribution system applications. It is important to note that in this embodiment of the invention, the end-to-end withstand voltage rating of each of the encapsulated vacuum switches 4' and 4" is at least 200 percent as great as the withstand. voltage rating of such switches would be in their unencapsulated state, due to the end-to-end insulation of conductors 8a 8a and l010", which is afforded by the insulating housing la and the insulating gas in sealed tank 16.

Of course, further modifications of the basic embodiments of the disclosed invention can be made by those skilled in the art, based on the teaching of the invention provided herein. Accordingly,it is my intent to encompass all such modifications and extensions within the scope and spirit of the following claims.

What I claim as new and desire'to secure by Letters Patent of the United States is: t

1. A high power electrical bushing having a vacuum switch encapsulated therein, comprising; an elongated molded housing of electrically insulating epoxy resin, said housing beingformed to have a frusto-conical surface at one end thereof for receiving an electric cable termination housing in water-tight relationship therewith, mounting means secured to said housing at a point intermediate the ends thereof for mounting saidhousing in rigid relationship in an aperture, said mounting means comprising an annular steel flange, the inner circumferential surface of which is molded in watertight relationship within said epoxy housing and the outer peripheral edge of which is adapted to be welded to a steel supporting flange, a vacuum switch mounted within said housing, said switch comprising a generally cylindrically-shaped, hollow, ceramic wall member, first and second metal end caps sealed respectively to opposite ends of said wall member thereby to define a vacuum chamber within the wall member, a first contact mounted in electrically conducting, fixed relationship on said first end cap, a second contact mounted on an electrically conductive, mechanically operable rod member for relative movement with respect to said second end cap, means defining an aperture through said second end cap for receiving the rod member therein, a flexible bellows mounted in sealing relationship between the second end cap and said rod member thereby to seal said aperture and said vacuum chamber while affording relative movement between the rod member and the second cap member, said rod member being mounted to extend predetermined distances beyond both sides of said bellows, and an electrical conductor mounted in said bushing and connected between said first end cap and the small diameter end of said frusto-conical surface, whereby an electrical circuit is formed through the contacts of said switch, when they are in engagement, from one end of said bushing to the other end thereof, the end-to-end length of said bushing being at least twice as great as the length of said switch between the first and second end caps thereof, and the dielectric strength of said epoxy resin surrounding said switch being sufficient to prevent electrical puncture thereof when it is subjected to a voltage greater than that required to flash over said switch in its unencapsulated state, thereby to enable the switch to be used to interrupt such a voltage when it is applied across the ends of said bushing.

2. An invention as defined in claim 1 including a generally cylindrically shaped hollow shield mounted on said first end cap and extending beyond the inner end of said first contact, th inner end of said shield being terminated in a plane that is positioned between said contacts when the movable contact is in its maximum spaced-apart relationship with respect to the first contact.

3. An invention as defined in claim 1 wherein said first contact is formed of copper and said second contact is formed of an anti-welding alloy of copper and one to 5 percent bismuth.

4. An invention as defined in claim 1 wherein said epoxy resin is a soft epoxy that forms a void-free seal with said vacuum switch.

5. An invention as defined in claim 1 wherein said epoxy resin is a hard epoxy, and including a layer of resilient sealing material mounted between said bushing and the wall member of said switch thereby to form a void-free junction between the bushing and said wall member.

6. An invention as defined in claim 5 wherein said layer is in the'range of 0.003 inch to 0.04 inch thick over its entire area.

7. An-invention as defined in claim 1 wherein said epoxy resin is at least 0.13 inch thick'over the entire surface of said ceramic wall member.

8. A multi-terminal high power electrical bushing having a pair of vacuum switches encapsulated therein,

comprising; a molded housing of electrically insulating epoxy resin, said housing being formed to have a pair of frusto-conical surfaces extending from the outer surface thereof at spaced-apart points on said surface, each of said formed surfaces being adapted to receive an electrical cable termination housing in water-tight relationship therewith, a steel flange molded partially into said housing and extending around an outer perimeter thereof, a steel tank, the outer portion of said flange being welded to said tank, thereby to position one end of said molded housing within said tank and to form a gas-tight seal around said one end of the molded housing, an electrical insulating gas disposed in said tank around said one end of the molded housing, each of said vacuum switches comprising; a generally cylindrically shaped, hollow ceramic wall member, first and second metal end caps sealed respectively to opposite ends of said wall member thereby to define a vacuum chamber within the wall member, a first contact mounted in electrically conducting, fixed relationship on said first end cap, a second contact mounted on an electrically conductive, mechanically operable rod member for relative movement with respect to said second end cap, means defining an aperture through said second end cap for receiving the rod member therein, a flexible bellows mounted in sealing relationship between the second end cap and said rod member thereby to seal said aperture while affording relative movement between the rod member and the second cap member, each of said rod members being mounted to extend into said tank, and a pair of electrical conductors mounted respectively in one of the frusto-conical portions of said molded housing to form a pair of electrical circuits from the respective first end caps to the small-diameter ends of said surfaces, and a mechanically operable mechanism mounted in said tank and connected to said rod members for moving them to open and close said pair of first and second contacts.

9. An invention as defined in claim 7 wherein each of said vacuum switches has an end-to-end withstand voltage rating in its encapsulated state that exceeds its end-to-end withstand voltage rating in its unencapsulated state by a factor of at least 200 percent.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,812,314 Dated MAY 21,

Inventor(s) GORDON C. NONKEN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 7, 4 4 BEFORE "PER METER" INSERT OUTER II II H II 7, 55 BEFORE WALL INSERT CERAMIC 8, M4 19 AFTER "APERTURE" CANCEL FROM "sAlo MOUNTING MEANs......suPPoRT|NG FLANGE" Bigncd and Scaled this twenty-fifth Day Of May 1976 [SEAL] Arrest:

RUTH c. MASON c. MARSHALL DANN Afltfling Officer Commissioner of Patents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,812,31 D t d MAY 21,

Inventor(s) GORDON C. NONKEN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C01 7, M4 5 E FOR E "PE R M E T E R I NS E RT OUTE R II I! II II 7, 55 BEFORE WALL INSERT CERAMIC 8, MI 19 AFTER "APERTURE" CANCEL FROM "SAID MOUNTING MEANS......SUPPORTING FLANGE" Signed and Sealed this twenty-fifth Day of May 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN AIM-fling off 're Commissioner uflalems and Trademarks 

1. A high power electrical bushing having a vacuum switch encapsulated therein, comprising; an elongated molded housing of electrically insulating epoxy resin, said housing being formed to have a frusto-conical surface at one end thereof for receiving an electric cable termination housing in water-tight relationship therewith, mounting means secured to said housing at a point intermediate the ends thereof for mounting said housing in rigid relationship in an aperture, said mounting means comprising an annular steel flange, the inner circumferential surface of which is molded in water-tight relationship within said epoxy housing and the outer peripheral edge of which is adapted to be welded to a steel supporting flange, a vacuum switch mounted within said housing, said switch comprising a generally cylindrically-shaped, hollow, ceramic wall member, first and second metal end caps sealed respectively to opposite ends of said wall member thereby to define a vacuum chamber within the wall member, a first contact mounted in electrically conducting, fixed relationship on said first end cap, a second contact mounted on an electrically conductive, mechanically operable rod member for relative movement with respect to said second end cap, means defining an aperture through said second end cap for receiving the rod member therein, a flexible bellows mounted in sealing relationship between the second end cap and said rod member thereby to seal said aperture and said vacuum chamber while affording relative movement between the rod member and the second cap member, said rod member being mounted to extend predetermined distances beyond both sides of said bellows, and an electrical conductor mounted in said bushing and connected between said first end cap and the small diameter end of said frusto-conical surface, whereby an electrical circuit is formed through the contacts of said switch, when they are in engagement, from one end of said bushing to the other end thereof, the end-to-end length of said bushing being at least twice as great as the length of said switch between the first and second end caps thereof, and the dielectric strength of said epoxy resin surrounding said switch being sufficient to prevent electrical puncture thereof when it is subjected to a voltage greater than that required to flash over said switch in its unencapsulated state, thereby to enable the switch to be used to interrupt such a voltage when it is applied across the ends of said bushing.
 2. An invention as defined in claim 1 including a generally cylindrically shaped hollow shield mounted on said first end cap and extending beyond the inner end of said first contact, th inner end of said shield being terminated in a plane that is positioned between said contacts when the movable contact is in its maximum spaced-apart relationship with respect to the first contact.
 3. An invention as defined in claim 1 wherein said first contact is formed of copper and said second contact is formed of an anti-welding alloy of copper and one to 5 percent bismuth.
 4. An invention as defined in claim 1 wherein said epoxy resin is a ''''soft'''' epoxy that forms a void-free seal with said vacuum switch.
 5. An invention as defined in claim 1 wherein said epoxy resin is a ''''hard'''' epoxy, and including a layer of resilient sealing material mounted between said bushing and the wall member of said switch thereby to form a void-free junction between the bushing and said wall member.
 6. An invention as defined in claim 5 wherein said layer is in the range of 0.003 inch to 0.04 inch thick over its entire area.
 7. An invention as defined in claim 1 wherein said epoxy resin is at least 0.13 inch thick over the entire surface of said ceramic wall member.
 8. A multi-terminal high power electrical bushing having a pair of vacuum switches encapsulated therein, comprising; a molded housing of electrically insulating epoxy resin, said housing being formed to have a pair of frusto-conical Surfaces extending from the outer surface thereof at spaced-apart points on said surface, each of said formed surfaces being adapted to receive an electrical cable termination housing in water-tight relationship therewith, a steel flange molded partially into said housing and extending around an outer perimeter thereof, a steel tank, the outer portion of said flange being welded to said tank, thereby to position one end of said molded housing within said tank and to form a gas-tight seal around said one end of the molded housing, an electrical insulating gas disposed in said tank around said one end of the molded housing, each of said vacuum switches comprising; a generally cylindrically shaped, hollow ceramic wall member, first and second metal end caps sealed respectively to opposite ends of said wall member thereby to define a vacuum chamber within the wall member, a first contact mounted in electrically conducting, fixed relationship on said first end cap, a second contact mounted on an electrically conductive, mechanically operable rod member for relative movement with respect to said second end cap, means defining an aperture through said second end cap for receiving the rod member therein, a flexible bellows mounted in sealing relationship between the second end cap and said rod member thereby to seal said aperture while affording relative movement between the rod member and the second cap member, each of said rod members being mounted to extend into said tank, and a pair of electrical conductors mounted respectively in one of the frusto-conical portions of said molded housing to form a pair of electrical circuits from the respective first end caps to the small-diameter ends of said surfaces, and a mechanically operable mechanism mounted in said tank and connected to said rod members for moving them to open and close said pair of first and second contacts.
 9. An invention as defined in claim 7 wherein each of said vacuum switches has an end-to-end withstand voltage rating in its encapsulated state that exceeds its end-to-end withstand voltage rating in its unencapsulated state by a factor of at least 200 percent. 